Decurling apparatus

ABSTRACT

Decurling apparatus for controlling the curl characteristics of a web incorporates a pair of elongated decurling rollers over a selected one of which the web may be drawn to produce a modification of its curl tendency. The magnitude of the curl tendency modification produced in the web is a function of the sharpness of the angle at which the web is drawn over the selected decurling roller. To vary the magnitude of the curl tendency modification being produced, the position of the selected decurling roller with respect to the web is varied to change the sharpness of the angular path of the web over the decurling roller. A movably mounted compensating roller over which the web is drawn is repositioned in response to movement of the selected decurling roller to compensate for the tendency of decurling roller movement to change the overall web path length.

United States Patent [151 3,66 1,703

Shelor 1 May 9, 1972 {54] DECURLING APPARATUS ABSTRACT [72] Inventor; Clifford D, shelor, co in V Decurling apparatus for controlling the curl characteristics of A a web incorporates a pair of elongated decurling rollers over a 2 weswflco Corporation, New York selected one of which the web may be drawn to produce a [22] Filed; 30 1970 modification of its curl tendency. The magnitude of the curl Appl. No.: 23,588

Primary Examiner-Arthur D. Kellogg ArtorneyW. Allen Marcontell and Richard L. Schmalz tendency modification produced in the web is a function of the sharpness of the angle at which the web is drawn over the selected decurling roller. To vary the magnitude of the curl tendency modification being produced, the position of the selected decurling roller with respect to the web is varied to change the sharpness of the angular path of the web over the decurling roller.

A movably mounted compensating roller over which the web is drawn is repositioned in response to movement of the selected decurling roller to compensate for the tendency of decurling roller movement to change the overall web path length.

10 Claims, 4 Drawing Figures Patented May 9, 1972 3,661,703

2 Sheets-Sheet 1 IN VENIOR.

CLIFFORD D. SHELOR Patented May 9, 1972 2 Sheets-Sheet 2 INVISNTOR. CLIFFORD D. SHELOR DECURLING APPARATUS BACKGROUND OF INVENTION In the treatment and processing of fibrous webs, it is advantageous to employ a device for conditioning the web to control its curl characteristics. The curl characteristics of the web determine its aerodynamic properties which, in turn, substantially influence the ease with which the web is handled.

The effect of aerodynamic properties of the web is especially evident in the handling of web material at high speeds, particularly after the web has been cut into short segments. Undesirable curl characteristics tend to cause such short segments to fly off their intended path as they are being transported while advantageous aerodynamic properties assist in causing the web to travel along a desired path and properly come to rest in a desired place. Undesirable curl characteristics will also cause segments of the web to be difficult to stack mechanically due to unwanted impingement of one segment of web with an outtumed edge of another segment.

In many systems which treat webs and with which decurling devices are used, a preferred location for the decurling device is immediately adjacent the system along a portion of the web path length which is actively maintained in a predetermined registry with operating elements of the system. Under these circumstances, however, manipulation of the web by the decurling device to modify its curl characteristics tends to change the registration between the web and the elements of the system. In many systems, for example printing systems, this can not be tolerated. Consequently, decurling devices are usually located away from the system operating upon the web, along a portion of the web path length which is not to be maintained in any particular relationship with elements of the system.

SUMMARY OF THE INVENTIONS The decurling apparatus of this invention conditions a web to have a particular curl characteristic without influencing the length of the web path. The web is drawn over an elongated decurling member which alters an undesirable curl characteristic of the web by imparting to the web a curl tendency which corrects the undesirable curl tendency. The magnitude of the correcting curl tendency imparted to the web is a function of the sharpness of the angular turn of the web as it is drawn over the decurling member. The position of the decurling member is adjustable to vary the sharpness of the angular turn of the web thereover and thereby variably control the magnitude of the correcting curl tendency imparted to the web.

Compensating means is provided to alter web path geometry in response to movement of the decurling member. This change in web path geometry compensates for the change in web path geometry necessarily produced by movement of the decurling member. The compensation is in a manner which avoids change in web path length as the position of decurling member is adjusted.

The decurling device of this invention is therefore usable along the active web path length of a system without influencing the relationship between the web and the system.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partially cut away perspective view illustrating a preferred embodiment of this invention;

FIG. 2 is a cross-sectional view of the preferred embodiment of FIG. I, taken along line 2-2 of FIG. 1;

FIG. 3 is a schematic view showing the apparatus of FIG. 2 in another position; and

FIG. 4 is a schematic view showing the apparatus of FIG. 2 in still another position.

DESCRIPTION OF A PREFERRED EMBODIMENT The illustrated preferred embodiment of this invention will be described. Referring to FIGS. 1 and 2, the decurling unit 16 for operating upon a web 12 includes a support means 22 which rests upon a base 24. The support means mounts an elevator means 32, a compensating means 38 and a drive means 40. Base 24 rotatably supports a pair of turn rollers 26 and 28 and also a resilient drive roller 30 which is mounted ad jacent the turn roller 28 to form a nip through which the web 12 may be drawn. Elevator means 32 supports decurling rollers 34 and 36 and varies the position of the decurling rollers in response to operation of the drive means 40. Included within the drive means 40 is a reversible motor 42, a sprocket 44, a chain 46, a sprocket 48 for rotating a shaft 50 and a pair of gear boxes 52 each housing a gearing mechanism, not shown, driven by the shaft 50. The elevator means 32 includes a pair of threaded shafts 59 extending from cooperative relationship with the gearing mechanism in each gear box 52 for reciprocally operating a pair of carriage plates 54. The carriage plates rotatably support the decurling rollers 34 and 36. The ends of the decurling rollers are journaled into bearings means 55, one such bearing means being mounted upon each carriage plate 54. The diameter of the decurling rollers is small relative to the diameter of rollers 26, 28 and 30.

The gap between the rollers 34 and 36 is greater than the thickness of the web 12 so that either the roller 34 may engage one side of the web or the roller 36 may engage the other side of the web, or so that the web may pass between the rollers without being engaged by either of them. Each carriage plate 54 is mounted for axial movement along a rigid carriage rod 56 which is firmly mounted to the support means 22. Bushings 58 provide the necessary support for the carriage plate 54 while permitting movement thereof along the rigid carriage rod 56. When the reversible motor 42 is driven in one direction, the drive means 40 will drive the threaded shaft 59, and thus the carriage plates and the decurling rollers from the condition illustrated in FIG. 2 wherein neither of the decurling rollers engages the web 12 to the condition illustrated in FIG. 3 wherein the decurling roller 34 is positioned to operate upon the web. Conversely, when the reversible motor 42 is driven in the opposite direction, the drive means 40 will lift the threaded shafts to lift both the carriage plates 54 and the decurling rollers 34 and 36 and thereby position decurling roller 36 for operation upon the web, as illustrated in FIG. 4.

When elevator means 32 advances the decurling rollers from the position of FIG. 2 toward the position shown in FIG. 3, the web 12 is contacted by the decurling roller 34 and the magnitude of the wrap of the web around the decurling roller 34 increases as the decurling rollers approach the position shown in FIG. 3. Conversely, movement of the decurling rollers from the position of FIG. 2 toward the position shown in FIG. 4 brings decurling roller 36 into contact with the web 12 and the magnitude of the wrap of the web 12 around the decurling roller 36 increases as the decurling rollers approach the position shown in FIG. 4. The amount of decurling action applied to the web by the decurling rollers increases as the wrap of the web around the rollers increases. It will be appreciated that operation upon the web by the decurling roller 34 produces a tendency to curl in one direction which compensates for an objectionable tendency of the web to curl in the opposite direction. Similarly, operation upon the web by the decurling roller 36 imparts to the web a tendency to curl in the aforesaid opposite direction to compensate for an objectionable tendency of the web to curl in the aforesaid one direction.

Variation in the position of the decurling rollers 34 and 36 necessarily effects a change in the geometry of the path of web 12. The change in web path geometry would produce a change in web path length between rollers 26 and 28 except for compensation provided by the compensating means 38. Such alteration of the web path length produces objectionable loss of registry between the web 12 and apparatus which operates upon the web either before the web reaches the unit 16 or after it emerges therefrom. The compensating means 38 responds to relative movement between the web 12 and the decurling rollers to change web path geometry in a manner which compensates for the tendency of web path length to vary when the aforesaid relative movement between the web and decurling rollers occurs.

The compensating means 38 comprises a pair of cam fol-' lowers 62 adapted to cooperate with the earns 60 formed in the carriage plates 54. The pair of cam followers 62 extend from a pair of cam follower shafts 64 mounted for reciprocation along their longitudinal axes by bearings 66. The cams 60 and cam followers 62 operatively interconnect the compensating means 38 and the elevator means 32. Depending from each of the cam follower shafts 64 and keyed thereto by means 70 is a support 68. Rotatably mounted between the supports 68 is a compensating roller 72 having a diameter larger than the diameter of the decurling rollers 34 or 36. In response to reciprocatory movement of the carriage plates 54 the cam follower shafts 64 reciprocate along their longitudinal axes and thereby cause the supports 68 and the compensating roller 72 to reciprocate. As shown in FIG. 2, the web passes over turn roller 26, between decurling rollers 34 and 36, around compensating roller 72 and then through the nip between turn roller 28 and resilient drive roller 30. As seen in FIG. 2, the apparatus is in a neutral position wherein the web is not operated upon by the decurler 16.

In the condition illustrated in FIG. 3, the decurling roller 34 is in position for engaging one surface of the web 12 for imparting to the web the maximum tendency to curl in one direction. The condition of FIG. 3 is achieved by driving the elevator means 32 to its full downward position. In response to this motion of the elevator means 32, the cam followers 62 and the cam follower shafts 64 are drawn by portion 60 of cams 60 along a path substantially normal to the path of the elevator means to draw the supports 68 and the compensating roller 72 toward turn roller 26. The change in web path geometry produced by the compensating roller 72 compensates for that produced by the decurling roller 34. Therefore, no change in web path length results. In the condition illustrated by FIG. 4, the other surface of web 12 is engaged by decurling roller 36 impart to the web 12 the maximum tendency to curl in the other direction. When decurling roller 36 is selected for use, the portion 60" of cam 60 controls movement of the compensating roller 72.

The character of the compensation provided by the motion of the compensating roller 72 is dependent upon the shape of cams 60. Accordingly, a discussion will follow setting forth the general manner in which the shape of the cam 60 in the preferred embodiment was determined. The general layout of the decurling apparatus was formulated and sketched. That is, the sizes and relative positions of all the elements influencing web path geometry and length were determined. Two reference points were then chosen, one on each side of the decurling roller, between which the web path length is to be maintained constant as the decurling roller is moved. For convenience in computations, the loci of the points should be close as possible to the decurling roller. In the preferred embodiment, these points are A and B. Point A is located where web 12 tangentially contacts fixed turn roller 26 and point B is located at the center of the nip where web 12 passes between fixed turn roller 28 and resilient drive roller 30. The path of movement of the decurling rollers was then determined. A path along a line passing through the longitudinal axes of the decurling rollers perpendicularly thereof, substantially normal to the undefected path of the web between rollers 26 and 72, is preferred. Next, the identity of the roller which is movably mounted to compensate for movement of the decurling roller and the desired path of its movement is determined. Roller 72 was selected and movement along a path perpendicular to the direction of movement of the decurling rolls was chosen for simplicity.

An algebraic equation for web path length between the selected reference points A and B was written in terms of web path geometry. It should be observed that the equation must be solved separately to determine the cam shape to be associated with each of the decurling rollers. That is, the shape of the portion 60 of the cam 60 which governs the movement of roller 72 when the decurling roller 34 is in use and the shape of the portion 60" of the cam 60 which governs the movement of roller 72 when the decurling roller 36 is in use must be independently determined. This independent determination of the shapes of portions 60' and 60" of the cam 60 is required because the displacement of roller 72 to compensate for a given downward displacement of the elevator means 32, which brings decurling roller 34 in contact with the web 12, is not equal to the displacement of compensating roller 72 to compensate for an equal upward displacement of the elevator means to bring decurling roller 36 in contact with the web.

For the apparatus shown in FIGS. 1 and 2, the equation included terms for the radii of turn roller 26, a selected one of the two decurling rollers 34 and 36, compensating roller 72 and turn roller 28. Also included in the equation were terms for the spacing between turn roller 26 and the selected decurling roller, the spacing between compensating roller 72 and the selected decurling roller and the spacing between the compensating roller 72 and turn roller 28. Terms were also included for displacement of the selected decurling roller and displacement of the compensating roller 72. A term for the angle defined at the geometric center of compensating roller 72 by radial lines extending therefrom to the two points on the roller surface at which web 12 is tangent to the roller surface was included. A similar term for the angle formed at the geometric center of the selected decurling roller by radial lines extending therefrom to points on the surface of the decurling roller at which the web is tangent to the surface of the decurling roller was also included. A determination was then made of the exact web length between the two reference points. This length was set equal to the algebraic expression.

Numbers were then substituted for all equation terms which are constant. A number of displacement values for the decurling roller were then assumed. Utilizing each assumed value, the expression was solved by a trial and error process to determine corresponding displacement values for the compensating roller. The displacement values for the decurling roller were plotted against the displacement values for the compensating roller to determinethe shape of the portion of the cam 60 which governs the pattern of movement of the compensating roller 72 when the selected one of the decurling rollers is in use. In similar manner, the equation was solved a second series of times and the resulting values were plotted to determine the shape for the other portion of the cam 60 which governs the pattern of movement of the compensating roller when the other of the two decurling rollers is in use.

Operation of decurling unit 16 will now be described.

It will first be assumed that, in an initial condition, the web does not have any objectionable tendency to curl as it enters decurler 16. In this condition, the decurler is set in a neutral position, as shown in FIG. 2, wherein it performs no operation upon the web 12. The web 12 is drawn over the turn roller 26 and between the decurling rollers and 34 and 36. The decurling rollers are positioned so that the web passes therebetween without contacting the surface of either roller. After passing between the decurling rollers, the web is drawn over compensating roller 72 and through the nip formed by turn roller 28 and resilient drive roller 30. A certain length of web is obtained between point A at turn roller 26 and point B at turn roller 28. During operation of the decurling unit 16, the length of web between points A and B must remain constant to insure that systems preceeding or following unit 16 are free from change in the relative positions of the web and elements of the system.

It will next be assumed that the web begins to pass through the system with an undesirable tendency to curl upon itself in a counterclockwise fashion. This tendency is corrected by bringing decurling roller 34 into contact with the web so as to apply thereto a tendency to curl in a clockwise fashion. The magnitude of the clockwise curl tendency must equal the objectionable counterclockwise curl tendency to achieve full compensation. The result is a web having the desired curl characteristics. It may be desirable to provide a web entirely free of curl or it may be desirable to provide a web having a predetermined curl.

The magnitude of the compensating curl tendency applied to the web 12 by the decurling roller 34 varies in accordance with the amount of the surface contact between the decurling roller and the web as the web passes over the roller. The amount of compensating curl tendency increases as the area of contact between the decurling roller and the web increases and decreases as the area of contact between the web and the decurling roller decreases. Stated differently, the amount of curl tendency imparted to the web by the decurling roller increases or decreases with increase or decrease, respectively, in the sharpness of the angular turn in the path of the web over the decurling roller. Accordingly, as the decurling roller 34 first contacts the web, a relatively small amount of compensating curl tendency is applied thereto and as the position of the decurling roller is continuously changed to increase the sharpness of the angular turn in the path of the web over the decurling roller, the compensating curl tendency increases. The compensating curl tendency is so increased until it relieves the objectionable curl tendency. Then the web 12 emerges from the decurling unit having the desired curl characteristics. To advance decurling roller 34 into contact with the web 12, reversible motor 42 is actuated to cause drive means 40 to drive threaded shafts 59 downwardly, as seen in H6. 3, so that the decurling roller engages the web 12 to impart thereto a tendency to curl about itself in a clockwise direction. The decurling roller 32 is advanced downwardly until the angular path of the web over the decurling roller provides a compensating curl tendency of the desired magnitude. When the web 12 is without objectionable curl, motor 42 is cut off and the decurling roller 34 remains as then positioned. When conditions change and a compensating curl tendency of different magnitude is required, elevator means 32 is again operated to reposition the decurling rollers. FIG. 3 shows the apparatus of P16. 2 set to impart the maximum amount of clockwise compensating curl tendency to the web 12.

If the web 12 is characterized by an objectionable tendency to curl upon itself in a clockwise direction, the decurling apparatus 16 is operated in a manner similar to that described above except elevator means 32 is raised rather than lowered to bring decurling roller 36 into engagement with the web 12. The decurling roller 36 applies to the web a tendency to curl upon itself in a counterclockwise fashion so that it compensates for objectionable clockwise curl tendency. See FIG. 4.

As the decurling roller 34 or decurling roller 36 moves to change the path of the web 12, it changes the web path geometry in a manner which tends to lengthen the overall web path between points A and B. Actual change in the path length between these two points is avoided however, by shifting the position of compensating roller 72 in response to motion of elevator means 32. Cams 60, shaped in the manner described above, cause the cam follower shafts 54 to move along their longitudinal axes to reposition supports 68 and compensating roller 72 as the elevator means 32 moves the decurling rollers with respect to the web 12. Movement of the compensating roller 72 tends to shorten or lengthen the web path by an amount equal to the tendency of the decurling roller movement to lengthen or shorten, respectively, the web path. The

- overall length of the web path between points A and B thereby remains constant.

It will now be appreciated that this invention provides apparatus for decurling a web without influencing the web path length. It is to be understood, however, that the foregoing description is of a preferred embodiment and that the invention is not limited to the specific apparatus shown and described. Therefore, changes may be made in the described preferred embodiment without departing from the scope of the invention.

Iclaim:

1. Apparatus for decurling a continuously advancing web comprising:

a. a web path through said apparatus to be followed by a continuously supplied web of thin sheet material;

b. a first fixed position station along said web path near the entry thereof into said apparatus;

c. a second fixed position station along said web path near the exit thereof from said apparatus;

d. a pair of elongated, substantially parallel, relatively spaced decurling members disposed along, transversely of and oppositely adjacent said web path between said first and second position stations;

e. decurling member adjustment means for advancing said decurling members along an adjustment path substantially, parallel to a plane including the longitudinal axes of said decurling members, said adjustment path also being substantially perpendicular to said longitudinal axes, advancement in one direction from a neutral position being effective to produce engagement between one of said decurling members and one surface of said web to deflect said web path in a first direction and impart to such web one modification of its curl tendency and advancement from said neutral position in the other direction being effective to produce engagement between the other decurling member and the other surface of such web to deflect the web path in a second direction and impart to such web another modification of its curl tendency; and

. web path compensation means movably disposed along said web path between said first and second position stations and interconnected to the movement of said decurling members in a manner such that the linear distance along said web path between said first and second position stations remains a substantially constant quantity.

2. Apparatus according the claim 1 wherein said web path compensation means comprises:

a. a compensating roller;

b. means movably supporting said compensating roller adjacent said decurling members so that such web may be drawn thereover subsequent to passage of such web between said decurling members; and

c. means linking said supporting means with said adjustment means.

3. Apparatus according to claim 2 further comprising cam means associated with said adjustment means and engageable with said linking means for controlling movement of said roller means as said decurling members are advanced.

4. Apparatus according to claim 3 wherein said decurling members comprise a pair of cylindrical rollers rotatably mounted in spaced, substantially parallel relationship, said rollers having a diameter substantially smaller than the diameter of said compensating roller.

5. Apparatus for decurling a continuously advancing web comprising:

a. a pair of cylindrical decurling rollers mounted in spaced relationship and with their longitudinal axes substantially parallel to form a passage therebetween for such web;

b. means for advancing said decurling rollers along a path substantially parallel to a line passing through the longitudinal axes of said decurling rollers perpendicularly thereof, advancement in one direction from a neutral position being effective to produce engagement between one of said decurling rollers and one surface of said web to deflect the web path in a first direction and impart to such web one modification of its curl tendency and advancement from said neutral position in the other direction being effective to produce engagement between the other decurling roller and the other surface of such web to deflect the web path in a second direction and impart to such web another modification of its curl tendency;

c. a compensating roller;

d. means movably supporting said compensating roller adjacent said decurling rollers so that such web may be drawn thereover subsequent to passage of such web between said decurling rollers;

e. cam means associated with said advancing means for controlling movement of said compensating roller as said decurling rollers are advanced; and

f. means linking said supporting means with said advancing means, said linking means including a cam follower engageable with said cam means for imparting movement to said compensating roller in response to advancement of said decurling rollers, said movement of said compensating roller producing a change in web path geometry which compensates for change in web path geometry resulting from advancement of said decurling rollers to avoid change in web path length during advancement of said decurling members.

6. Decurling apparatus for use with means for advancing a web between a pair of predetermined loci comprising:

a. an elongated decurling member between said loci adjacent such web for imparting curl tendency to such web;

b. means movably mounting said decurling member for advancing said decurling member into engagement with such web to controllably produce change in the path geometry of such web, the magnitude of the curl tendency imparted to such web by said decurling member being a function of web path geometry;

c. compensating roller means;

d. means movably mounting said compensating roller means between said loci adjacent the path of such web to provide an adjustable support for such web; and

e. cam means linking said means movably mounting said decurling member and said means movably mounting said compensating roller means for producing predetermined movement of said compensating roller means in response to movement of said decurling member to influence web path geometry in a manner which maintains the web path length between said loci constant.

7. Decurling apparatus according to claim 6 wherein said decurling member comprises a roller having a diameter which is small relative to the diameter of said compensating roller.

8. Decurling apparatus according to claim 6 further comprising a second elongated decurling member spaced from the first said decurling member and disposed substantially parallel thereto to provide a passage for such web between said decurling members. 7

9. Decurling apparatus according to claim 8 wherein said first decurling member is advanceable from a neutral position into engagement with one surface of such web for controllably producing change in the path geometrty of such web and said second decurling member is advanceable from a neutral position into engagement with the other surface of such web for controllably producing change in the path geometry of such web.

10. Decurling apparatus according to claim 6 wherein said cam means comprises a cam surface associated with said means movably mounting said decurling member and a cooperating cam follower extending from said means movably mounting said compensating roller'means.

I l l 0' l 

1. Apparatus for decurling a continuously advancing web comprising: a. a web path through said apparatus to be followed by a continuously supplied web of thin sheet material; b. a first fixed position station along said web path near the entry thereof into said apparatus; c. a second fixed position station along said web path near the exit thereof from said apparatus; d. a pair of elongated, substantially parallel, relatively spaced decurling members disposed along, transversely of and oppositely adjacent said web path between said first and second position stations; e. decurling member adjustment means for advancing said decurling members along an adjustment path substantially, parallel to a plane including the longitudinal axes of said decurling members, said adjustment path also being substantially perpendicular to said longitudinal axes, advancement in one direction from a neutral position being effective to produce engagement between one of said decurling members and one surface of said web to deflect said web path in a first direction and impart to such web one modification of its curl tendency and advancement from said neutral position in the other direction being effective to produce engagement between the other decurling member and the other surface of such web to deflect the web path in a second direction and impart to such web another modification of its curl tendency; and f. web path compensation means movably disposed along said web path between said first and second position stations and interconnected to the movement of said decurling members in a manner such that the linear distance along said web path between said first and second position stations remains a substantially constant quantity.
 2. Apparatus according the claim 1 whErein said web path compensation means comprises: a. a compensating roller; b. means movably supporting said compensating roller adjacent said decurling members so that such web may be drawn thereover subsequent to passage of such web between said decurling members; and c. means linking said supporting means with said adjustment means.
 3. Apparatus according to claim 2 further comprising cam means associated with said adjustment means and engageable with said linking means for controlling movement of said roller means as said decurling members are advanced.
 4. Apparatus according to claim 3 wherein said decurling members comprise a pair of cylindrical rollers rotatably mounted in spaced, substantially parallel relationship, said rollers having a diameter substantially smaller than the diameter of said compensating roller.
 5. Apparatus for decurling a continuously advancing web comprising: a. a pair of cylindrical decurling rollers mounted in spaced relationship and with their longitudinal axes substantially parallel to form a passage therebetween for such web; b. means for advancing said decurling rollers along a path substantially parallel to a line passing through the longitudinal axes of said decurling rollers perpendicularly thereof, advancement in one direction from a neutral position being effective to produce engagement between one of said decurling rollers and one surface of said web to deflect the web path in a first direction and impart to such web one modification of its curl tendency and advancement from said neutral position in the other direction being effective to produce engagement between the other decurling roller and the other surface of such web to deflect the web path in a second direction and impart to such web another modification of its curl tendency; c. a compensating roller; d. means movably supporting said compensating roller adjacent said decurling rollers so that such web may be drawn thereover subsequent to passage of such web between said decurling rollers; e. cam means associated with said advancing means for controlling movement of said compensating roller as said decurling rollers are advanced; and f. means linking said supporting means with said advancing means, said linking means including a cam follower engageable with said cam means for imparting movement to said compensating roller in response to advancement of said decurling rollers, said movement of said compensating roller producing a change in web path geometry which compensates for change in web path geometry resulting from advancement of said decurling rollers to avoid change in web path length during advancement of said decurling members.
 6. Decurling apparatus for use with means for advancing a web between a pair of predetermined loci comprising: a. an elongated decurling member between said loci adjacent such web for imparting curl tendency to such web; b. means movably mounting said decurling member for advancing said decurling member into engagement with such web to controllably produce change in the path geometry of such web, the magnitude of the curl tendency imparted to such web by said decurling member being a function of web path geometry; c. compensating roller means; d. means movably mounting said compensating roller means between said loci adjacent the path of such web to provide an adjustable support for such web; and e. cam means linking said means movably mounting said decurling member and said means movably mounting said compensating roller means for producing predetermined movement of said compensating roller means in response to movement of said decurling member to influence web path geometry in a manner which maintains the web path length between said loci constant.
 7. Decurling apparatus according to claim 6 wherein said decurling member comprises a roller having a diameter which is small relative to the diameter of said compensating roller.
 8. Decurling apparatus according to claim 6 further comprising a second elongated decurling member spaced from the first said decurling member and disposed substantially parallel thereto to provide a passage for such web between said decurling members.
 9. Decurling apparatus according to claim 8 wherein said first decurling member is advanceable from a neutral position into engagement with one surface of such web for controllably producing change in the path geometrty of such web and said second decurling member is advanceable from a neutral position into engagement with the other surface of such web for controllably producing change in the path geometry of such web.
 10. Decurling apparatus according to claim 6 wherein said cam means comprises a cam surface associated with said means movably mounting said decurling member and a cooperating cam follower extending from said means movably mounting said compensating roller means. 